题解 | #按之字形顺序打印二叉树#

层序遍历，加个flag转向就行了

class Solution {
public:
    vector<vector<int>> Print(TreeNode* pRoot) {
        vector<vector<int>> res;
        if (!pRoot) return res;
        queue<TreeNode*> q;
        q.push(pRoot);
        bool rev = false;
        while (!q.empty()) {
            int n = q.size();
            vector<int> tmp;
            for (int i = 0; i < n; i++) {
                if (q.front()->left) q.push(q.front()->left);
                if (q.front()->right) q.push(q.front()->right);
                tmp.push_back(q.front()->val);
                q.pop();
            }
            if (rev) reverse(tmp.begin(), tmp.end());
            rev = !rev;
            res.push_back(tmp);
        }
        return res;
    }
    
};